1. Field of the Invention
The present invention relates to a method for calibrating a light traveling distance in a scanning module and, more particularly, to a method using transparent glass to increase or decrease the light traveling distance in a scanning module.
2. Description of the Prior Art
Platform scanners are commonly used in offices for converting paper documents into image data. The optical scanning module is the main scanning component within a platform scanner. A scanning module usually comprises a casing having an opening for receiving light transmitted from a scanned document, an optical sensing device installed in the casing for transforming the light transmitted from the scanned document into corresponding image signals, a plurality of mirrors for passing the light to the optical sensing device, and a lens for converging the light to the optical sensing device.
The resolution of a typical scanning module is constant and determined by the magnifying power of the scanning module as well as the resolution of the optical sensing device in the scanning module. The magnifying power of the scanning module is determined by the lens, by the distance from the scanned document to the lens, and by the distance from the lens to the optical sensing device. Therefore, if errors occur in the positioning or the angles of the lens or mirrors during the assembly process, the distance between the scanned document and the lens or the distance between the lens and the optical sensing device is altered thus biasing the magnifying power of the scanning module. Also, components in the scanning module such as the lens and optical sensing device have their own tolerances which may also affect the resolution of the scanning module.
When reduction of the allowable error tolerance range of the magnifying power, lens or the optical sensing device is required, the yield rate of scanners drops sharply and the number of calibrations increase dramatically. Thus the cost of the product increases.